Unfortunateley I am not quite sure of the correct terms, but I will describe it and maybe it makes sense.

When you push the breech locking lever top one side, this acts on a "slab" of metal that moves forwards and backwards underneath the barrels to engage with a lug that is on the bottom of the barrels.

The edge of this 'bar' or 'slab' has worn over the years because when the shotgun is closed, the lug on the barrels is slightly angled to push the bar open - the classic 'snap the gun shut' action we all know. Because of the wear, the rear face of the barrels do not sit tight against the action - in effect the barrels 'rattle' and I certainly dont want to fire it like this!

So I need to re-make this bar. Easy enough job using a milling machine, or by hand filing, but my question is what steel do I use? or should I use a mild steel but then case harden it?

The precise design of the bar means that the entire force it has to withstand during a discharge is taken through a cross section approximately 1/8 x 1/4 inch. I dont want to make it brittle by hardening it but I dont want the same fault to re-appear in a couple of years through wear of the unhardened metal.

ANy experts care to comment?

(By the way, I will be having the gun proofed after repair, before using it!)

This is some thing for a real gunsmith to anwser, not a backyard gunsmith on here .There is more to this than meets the eye. If you have a mill machine and everything you need to do this work AWESOME , but get your answers from a pro , not an internet junkie. Good luck with this rebuild ,it sounds cool!

Hi MikeI was hoping that I might find a 'pro' on this forum; i.e. a metallurgist or similar! Unfortunately where I live we dont have many true gunsmiths - they call themselves gunsmiths but they are nearly all just gun dealers, sending away any real work that needs doing! Needless to say they will all say the gun isnt worth repairing, which of course it wouldnt be if it was done professionlly, but its just my time really!

The barrels are not damascus though, so its not that old and they have previously been proofed for a nitro load.

Ok that make sence, Go to Doublegun.com you will for sure be able to get the info on there from a great bunch of guys and gals that know thier stuff when it comes to resto's. Good luck this sounds like a fun project!

i think you could make that piece out of regular Oil hardening tool steel commonly called O1

id make it just a tad larger all around, and heat it to 1550 F for about 15 minutes then quench in quenching oil ...

then temper in another oven at about 550 degree for 1 hour....this should give you a final hardness of about 55 rockwell.....certainly hard but not brittle hard...you could even go 600 and make it slightly softer maybe the low 50's rockwell..

then you will have to GRIND the final fit.....which will take some skill

it is possible to fit the part while still un hardened and then harden...... you shouldnt get too much change of shape on a big block of metal like that part.( i wouldnt do that on think and intricate parts though)

i know this sounds a little strange but put some scotch tape on the barrel hinge pin and then assemble the gun, most guns locks dont wear as much as the hinge, if this makes the gun tight again then you might just need to build up the "hook" or pin